Following on from last week's introduction to hydrocarbons, there is a great deal more complexity to organic compounds.
If all organic chemistry came down to simply adding one more carbon to a chain, it would be both easy and boring. Ask any student who has taken an organic chemistry course and they will tell you it is not easy.
First of all, there is branching. At four carbons in length, a hydrocarbon can be simple normal butane (C-C-C-C) but it is also possible to add a fourth carbon to the middle of a three carbon chain, resulting in a "Y" structure. This compound is called methyl-propane where methyl refers to a CH3 group and propane to the three carbon chain.
With five carbons, there are three possible arrangements or isomers (normal pentane, methyl-butane, and dimethyl-propane). The number of possibilities quickly escalates. For eight carbons, there are 18 possible isomers. For 20 carbons, there are 366,319 possible isomers. And for 30 carbons, there are 4,111,846,763 possible isomers.
The number of possible ways of arranging carbon and hydrogen into hydrocarbon compounds is astronomical - particularly considering polymeric chains such as polyethylene or polypropylene can contain hundreds of thousands of carbon atoms.
By themselves, carbon and hydrogen can lead to even more possible compounds. Instead of a simple covalent bond linking to carbon atoms together via the sharing of a single pair of electrons, it is possible for carbons to share two pairs resulting in a double bond (C=C instead of C-C).
Double bonds are rigid whereas single bonds are not. If you have ever danced a jive, you know you can easily spin a partner when holding only one hand but add the second one and the exercise becomes much more complicated. Both partners have to flip their bodies in unison and in the end you have the same orientation as you started with.
The same is true at a molecular level. Carbon-carbon bonds can spin around a single bond producing all sorts of wiggly configurations, but add a double bond and the spinning stops. The result is one of two locked-in possibilities - either cis or trans. This is where the term trans-fat comes from as the fatty acids have trans double bonds in their chains.
Hydrocarbons can have more than one double bond in a particular chain. They can also form triple bonds where the carbons share three pairs of electrons. They can even form rings which might multiple double bonds leading to compounds like benzene, toluene and xylene.
If the number of simple saturated hydrocarbons possible is astronomical, then the number of all possible hydrocarbons is astronomical raised to the power of astronomical. It is a very large and complex set of compounds.
Of course, organic chemical compounds can also incorporate other elements such as oxygen, nitrogen, sulfur, chlorine, bromine, iodine and fluorine.
Almost every one of the myriad of hydrocarbons could have any or all of its hydrogen atoms replaced by any and all combinations of these elements.
There are also functional groups such as acids, esters, ketones, aldehydes, amides and alcohols.
Organic chemistry is not easy.
With respect to petroleum in all its forms, from sweet crude to bitumen, there are a large number of different chemical compounds present. Typically, these are simple hydrocarbons mixed with benzene and toluene compounds and the occasional oxygen or nitrogen containing species.
This chemical soup might contain upwards of 1,000 compounds but not anywhere near as many as are actually possible. To be useable for most applications, all petroleum must be refined. The processes involved adjust the balance between long chain and short chain molecules.
For example, gasolines typically have molecules in the five to 10 carbon categories. Long chain molecules with, say, 20 carbon atoms can be cracked giving molecules more suitable for gasoline.
Similarly, a butane and a methyl-propane can be joined together to give an eight carbon species.
Manipulating the length of carbon chains, the number of double bonds, the types of side chains, and such is what petroleum chemistry and engineering is all about. The idea is to modify crude oil to get a mixture which meets market demands.
Bitumen happens to be a version of petroleum with a lot more long chain compounds than short. This is why it presents as a tar or thick, viscous liquid.
Converting the tar to shorter chain molecules can lead to everything from gasoline and jet fuel to lighter fluid and polyethylene. Diluting the long chains with shorter chains creates a thinner liquid capable of flowing through pipelines
But if a spill does occur, the lighter fractions will evaporate leaving the heavy tar which is dense enough to sink to the bottom of a waterway. While dilbit really isn't any different from other crude oil, it is the potential to return to an organic tar which leaves open questions about its safety.
